1. Field of the Invention
The present invention relates to an active matrix liquid crystal display device and the like.
2. Description of the Related Art
Conventionally, an active matrix liquid crystal display device using an active element such as a thin film transistor (TFT) has been known. In an active matrix liquid crystal display device, pixel density can be heightened. In addition, an active matrix liquid crystal display device is small and lightweight, and consumes low power. Accordingly, products such as a monitor for a personal computer, a liquid crystal television, and a monitor for a car navigation system have been developed as one of flat panel displays in substitution for a CRT.
In a liquid crystal display device, display is conducted in the following manner: a substrate (an active matrix substrate) provided with a pixel portion including a first electrode (a pixel electrode) and the like in addition to a plurality of TFTs and a wiring and a substrate (an opposite substrate) provided with a second electrode (an opposite electrode), a light-shielding film (a black matrix), a colored film (a color filter), and the like are attached to each other; a space between these substrates is filled with a liquid crystal and sealed; and liquid crystal molecules are oriented by an electric field which is applied between the pixel electrode and the opposite electrode to control the amount of light from a light source.
However, it is necessary to conduct alignment with favorable accuracy in attaching the active matrix substrate and the opposite substrate to each other. If the alignment is insufficient, misalignment is caused between the pixel electrode over the active matrix substrate, and the colored film or the light-shielding film over the opposite substrate. This results in reduction in contrast due to light leakage in addition to out of color registration and a blur in an image in displaying, and accordingly, a problem of display with poor visibility is caused.
Concerning this issue, a manufacturing method of a liquid crystal display device is reported as follows: a colored film and a light-shielding film which are conventionally formed over an opposite substrate are formed over an active matrix substrate, and in a step of manufacturing any of a switching element, a colored film, and a light-shielding film, a first marker (an alignment marker) formed using metal or a resin film over the active matrix substrate and a second marker (an alignment marker) formed by coating the opposite substrate with a conductive paint material are compared, whereby alignment with favorable accuracy is possible in attaching the substrates to each other (refer to Patent Document 1: Japanese Published Patent Application No. 2002-350800).
However, the formation of the markers (the first marker and the second marker) for alignment over the active matrix substrate and the opposite substrate, respectively, in an additional step is one of the factors for further reduction in yield in manufacturing a liquid crystal display device and the like through a complicated process. Moreover, a problem that alignment accuracy is lowered and an inspection process for alignment requires much time occurs as a panel is enlarged.